Previous studies showed that in the intact rat chromaffin cells are insensitive to the presynaptic stimulatory toxin, alpha-latrotoxin (alpha-LTx). In contrast, primary cultures of rat adrenal chromaffin cells respond to alpha-LTx by releasing stored catecholamines. The toxin-induced response was greater in cultures from young (8-10-day-old) than adult (40-50-day-old) animals, and increased when the time of culturing was prolonged from 4 to 20 days. Even greater responses were observed in cells cultured in the presence of nerve growth factor, a treatment which induces a neuronal-like phenotype. Acquisition of sensitivity to alpha-LTx appears to be an early marker of chromaffin cell commitment to differentiate towards a neuron.